Method and apparatus for producing a helical magnetic sound track on a wire record



Jufie 0 H E. TOMPKINS Er L A METHOD AND APPARATUS FOR PRODUCING A HELICAL MAGNETIC SOUND TRACK ON A WIRE RECORD Filed Oct. 9, 1945 2 Sheets-Sheet 1.

/0 m4 i /a?* lOZ PHASE l0 6 f ANPLlFlER 6 .7 PHASE I09 I I SHIFTER m7 lll 5 V INVENTORS 50 HOWARD E. TOMPK/NS v WILL/AM E. BRADLEY 0 6 a l 1.44,: a

' R v ATTORNEYS June 13, 1950 v H; E. TOMPKINS a-rm. 2,511,506

METHOD AND APPARATUS FOR PRODUCING A HELICAL MAGNETIC SOUND TRACK ON A WIRE RECORD Filed 001;. 9, 1945 2 Sheets-Sheet 2 INVENTORS HOWARD E. TOMPK/NS WILL/AM E. BRADLEY Patented June 13, 1950 METHOD AND APPARATUS FOR PRODUCING A. HELICAL MAGNETIC. SOUND TRACK ON A WIRE RECORD Howard E. Tompkins, -Medim and William E. r. 1 Bradley, SwarthmoregPa zassignors', bymesne v assignments, to .Philco; Corporation; Philadelphia, Pa., a corporation ofBennsylvania 1' Applicationflctober 9,1945; Serial No; 621 *,292

15 Claims.

diificulty isencountered in the. reproduction of l. the sound orother intelligence from the. record on thewireibecause of thecircu1ar cross-section of the. wire; This circular crossasection. makes .it-possible'forthe wire to twist upon its longi- 4 tudinal axis. -Consequently, .itlis possible during reproduction: for the wire to twist to such an extent that the magnetization of the wire is at rightanglesto the pick-up coil of the reproducer. Under these circumstances, nosignal is obtained from the wire.

:Various arrangements have been suggested for overcoming such adiificultya One such arrangement involve thesuse or automatic volume control in the ampl-ifierybut this autpmaticvolume control. ceases to function when the wire ha rotated aiull 90: .from the pick-up. coil.

1 Anothenmethod whichhasbeen suggested fo overcomingthis-iiifiiculty employs an automatic vi follow -up system whereby the pick-up coil ware caused to rotate around the longitudinalaxis of a the wire-in synchronism-with the twisting of the w wire.- Such a mechanism, while accomplishing the result is unduly and unnecessarily subject to high maintenance cost and -easy possible failure.

.l Inaccordancewith our invention, it is possible to record-transversely upon the round magnetic wire such a manner'that twisting of the wire is unimportant asiar asthe reproduction of the signals is concerned.

In general, we effect transverse recording in a helical manner upon the round wire. That is,

r as a single frequency is impressed uponthe recorder, the-:magnetization in the wire is caused to progress helically along the wire-instead of being in one direction in the cross-section only. When a record which has been recorded helically is'reproduced by an ordinary type of reproducer for transverse recording, the angular orientation ofthe wire 'isiminaterial except as it produces a possible slight change in ==phase with respect he tothe-recorded signal; 1 However, it is well known that slight changes in phase angle are unimportant as far asithe ear is concemed. Consequently forthe recording of sound, no distortio is produced byhelical recording.

When several frequencies are:combined.iinlthe a-signal to be ..recor.ded, ieach;drequency is; caused 4.1 .to record in ahelical manner; independently of .1 the other :frequencies. rrl'Fonjeach frequencypthe :5: -:pitch' ofatherhelix, along; theiwire isasuch that in .nonei period ofsthesfrequencybeing;recorded;:the magnetization :hasrotateda once: around .the; wire. Consequently, foraeachefnequency beingrecorded, .1 theepitch on: the. wine; thatrisrlthadistanc'ej along the. wire f0]?.0118,BOm PIEtLELTEVOIHtiOD. of zthe; wire magnetization is: dilterentx for slow. frequencies, he pitch .isilong, for; high frequenciesethe .pitch sshort. when. amending-made imthismannenis re- 1.5::prncluced by; an :orclinaryv type lot transverse reproducer sothelpickeupahead has generated in it oltageshcorresponding liOjith-Q'ISHIII of themag- 41' netizations of;v eachufrequency involved in. the ,yarecording on =the1vvire. That is,,:the waveashape 20 of. the .voltagexin the. pick-up :coil, Will. be ;;that which would be obtained by thasummation of ---z:-;wavelshapes or the; corresponding rsfrequencies n;: .which are recorded.

irsince ;each of .these recorded; frequencies .has 5 itsown pitch: along theamagneticr-wire; thephase .relationship of the: various frequencies will differ :1 l :as.the wirerotates in the Pick-up head that is, ,aszthe. wire-rotates about it -longitudinal, axis in .accordance. With rwhateverwtwistymay beset up \by. the reproducin -machine.

i :l-Iowever, in.-,vie w .ot thefactthat, the ear is 311101}, sensitive to-esmallhchanges in, phase gangle ,:,;betweenithe various-frequency vcomponents of a i. 1;- ;signal; this. shift imphase angle. as the wireztwists in the-recorder .1011; reproducerdoesnot .causedany serious a difficulty :in' the understandingof; the reproduced- .:signal.:,. In iaot, .the ear-sis; insensitive tothisaction. :1 i As ;a-. result of.-ourinventionvthen, itazbecomes ,;p0ssib1:e. to; use :ro lndawires for. transverse imagnetietrecording and to use a ,very;;simple reproducing-mechanismforreproducing the record into 1: sound.

1c. Accordingly; an; object oflour invention is to -;provide1a means forzrecordingz transversely upon round'magnetic, wire in isuchgatimanner as to 'laNOidti difiiculties :reproduction .z-idue to;.i:the 5.: twisting of the wire.

A nother object ofiour invention is to #provide 5 means for using transverse recording upon round magnetic wire.

1* These objects'andother objects of our invention "'will'become evident upon study of the following .drawings', in which: 6o Figure 1 represents a helicaltype orrecordand its association to the pick-up coil in the reproducer;

Figure 2 represents the principle of the recording head;

Figure 3 shows in block diagram the of the complete recorder;

Figure 4 shows the characteristics of the phase shifting network in Figure 3; and

principle Figure 5 shows detailed circuit of the block diagram of Figure 3. 7

Referring to Figure 1, the round magnetic wire I00 is shown as broken at its two ends to indicate that the wire is considerably longer than is shown in the figure. The helical line IOI along-and around this wire I00 represents the location of the magnetization which would result from a sinusoidal signal being impressed upon the wire according to our invention. This line IOI represents the location of the maximum magnetization and it is to be understood that the magnetization is transversein the wire.

For. example, immediately under the pick-up coil I02, the flux lines I03 and I00 are shown as entering at the bottom of the wire and leaving L the wire at thetop, having passed through the wires These fiux lines are the result of magnetization in the wire existing in the direction of the flux line within the wire.

.Thus, where flux lines I03 leave the wire, there exists upon the surface of the wire a north magnetic pole and where flux lines I04 enter the wire,

. there exists upon the wire a south magnetic pole.

The location of the north magnetic pole, in accordance withmy method ofrecording, rotates spirally or helically along the .wire in accordance with the line IOI drawn upon the surface of this wire. The corresponding location of the south pole is not shown on the diagram as this is understood-to be always diametrically opposite to the location ofthe north pole as the north pole spirals along the wire.

As the .wire I00 is moved through the reproducer in accordance with the arrow of direction I05, thevoltage magnetically induced in coil I02 varies in accordance with the rate of change ofmagnetic fiux through the core of coil I02. Thus since the flux through coil I02 is going through a maximum and consequently is notchanging 'at'all.-- As wire I00 is passed under the coil I02, a sinusoidal voltage is induced in coil I02 with a frequency proportional to the velocity of the wire and inversely proportional .to the length along the wire required for the direction of mag- A netization to be rotated completely through 360 since otherwise, a change in frequency of the recorded signal would occur. However, in practice, the twists which occur in the wire- I00 do have that property-that is, they are relatively gradual.

twists. N

In order to record a signal such as is shown in Figure 1 upon a wire, a structure symbolized by Figure 2 is used. This'structure i's-very similar to the type of structure used for a two-phase voltas the wire passes the position shown in Figure 1, there novoltage is being generated in coil I02 age and is shown in Figure 2 in its most elemental form. Two magnetizing coils and associated magnetic yokes I06 and I01 are employed.

The signals feeding these two coils are arranged to be 90 out of phase with each other. As is well known in motor theory, such a signal applied to such a magnetic structure will cause a revolving magnetic flux vector in the wire I00. In ordinary two-phase motors, this revolving magnetic field is the agency which causes the motor to rotate.

In this system of magnetic recording however, this rotating magnetic flux vector magnetizes the wire I00 in the helical method since as the magnetic flux vector is rotating, the wire is moving through the recording head at the same time. The combination of the motion of the wire past the recording head and the rotation of the magnetic flux causes the helical magnetization shown in Figure 1.

When more than one frequency is involved, as

it usually is in the reproduction of any type of sound other than a pure note, the signals impressed upon coils I06 and I01 are made up of as many frequency .waves as can be resolved from the complex sound wave.

In order for this magnetization to produce helical recording for each frequency component, it is necessary that the signals impressed upon coils I00 and I01 in Figure 2 partake of the fixed 90 phase shift between several frequency components and must achieve this fixed phase relation over a wide range of frequencies. For sound recording, it must accomplish this purpose over a substantial portion 00 the audio-(frequency band.

If such a 90 angle is maintained over the operating frequency range, the signal recorded upon the wire I00 (Figure 2) will consist of a series of helical signals, each frequency of which will cause a rotation or helical path of magnetization upon the wire I00 independent of each other frequency. When the record is reproduced, as is shown in Figure 1, the pick-up coil I02 will then be energized by each of the individual frequencies separately and signals of these frequencies will be combined in the output system. Phase relationships between .the frequency components will depend upon the angular position of the wire. It has beenwell established, however, that the ear is insensitive to moderate phase variation, and consequently the randomness of the phase in this circumstance doesnot constitute any difficulty in the interpretation of the output sound.

In, order to achieve the 90 phase shift of the signal, as is required for Figure 2, the circuit as shown in block diagram form in Figure 3 is em ployed.,-Voice or, other signals enter the microphone I08. These signals are amplified by the amplifier I09 toa sufiicient level to operate the recorder. These signals are split into two channelsone channel going-to phase shifter H0 and another channel going to phase shifter I I I. Signals from phase shifter IIO are sent to magnetizing coil I06'and signals from phase shifter I I l' are sent to magnetizing coil I01. The special property ofthe'phaseshifters IIO andlll is such that over the audio-frequency range, the

difference in phase, shift-between thesetwo phase shifting networks is Thus, although phase shifter IIO shifts the phase of the signal from amplifier I09 for different amounts for each frequency involved, -.for' any frequency within the audio-range, the phase'shift' occurring in network I! I is 90 mor'(0r1ess)"th'an the phase shift occurringjn' phase shifter-II 0.1 Consequently, for any frequency withinthe audio'range, the signals tially at. 120 intervalsand three phase shifters designedfor 120 phase angledifferencesprovide a rotating magnetic flux vector in the same manner that. the stator of a three-phase induction motor provides a rotating magnetic flux vector. Moreover, in. one form of our' invention, the mag netic circuits. are constructed-together as-a single unit in. amanner similar .to that customarily employed in: the manufacture of induction motors.

Figure 4 shows the phase shift curve obtained in one circuit which hasbeen used for the block diagram of Figure 3. Phase shifter H0 'has a phase shift in accordance with-curve--55--in Figure 4. The lower channel, that is phaseshifter I I I,

For

has a phase shift in accordance with curve 58 in Figure 4. Consequently th'ephase angle difference between these two curves is given by curve SI. Inspection of this curveindicates that from a frequency of about 45 cycles-per second to 12,000 cycles per second, the phase angle does not vary more than 10 from the nominal value of 90, and that for most of the range, the phase angle is considerably closer to 90 than this tolerance of 10. Such a tolerance is sufilciently good for helical recording: since this is a barely audible variation in the amplitude of therecorded signal.

In Figure 5 there is shown a detailed circuit diagram of the network used to obtain the curves of Figure 3. In the upper channel, two bridges 03 and A5 are placed in tandem. In accordance with the invention of Tompkins, described in copending application, Serial No; 613,457, filed August 1945, bridge-43 is alow impedance bridge and bridge 45 is a high impedance bridge in accordance with the principles set forth in connection with the above-mentioned application. The output of bridge "4515 sent into a differential amplifier 47, which. is loadedwith low impedance bridge 49.. This bridge 49 is fed from a high impedance source and feeds into a low impedance circuit following the principles set down for a bridge of this type in the above-mentioned patent application. This bridge 49 feeds into the recording coil I06 which records on the wire I00.

The impedance of coil I06 should, at all frequencies in the audio-spectrum, be low compared to the impedance looking back into the output of bridge 40 in order to meet the requirements of this bridge.

The lower channel is composed of a similar chain of elements: two bridges 44 and 46 followed by a difierential amplifier 48, followed by another bridge 50 and feeding it to recording coil I 01. In this current arrangement, both channels are fed from a common source which in order to provide a low impedance source is a cathode follower circuit 54, which is itself fed by the audio signal to be recorded.

The constants of these two bridge circuits are so chosen to give the curves shown in Figure 4 with the result that the signals applied to the two magnetizing coils I00 and I 01 are substantially 90 out of phase With each other over the whole audio-spectrum.

'lhe result is helical recording which makes it 63' possible to reproduce the recording. in any'ordie nary type of reproducer for use with transverse: recording.

Our invention, which we have described above, relates to a particular embodiment of our method: of helical recording on round magnetic wire. It is, of course, possible to accomplish this helical; recording by various types of specific networks, Consequently, it becomes our desire to describe: our invention in terms of the following claims.

We claim:

1. In a system for recording sound on a mag-' netic wire of circular'cross-section, a pair of recording structures, amagnetic circuit and a mag-- netizing' winding for carrying magnetizing current individual to each of said pair of recording' structures, said recording structures being orient ed with respect to said wire to produce magnetic fluxes in mutually perpendicular directions at the same location, and means including network units connected to each of said windings for producing signals in each of said windings one of which is substantially in quadrature with respect to the other.

2. In' asystem' forrecording sound on a magnetic wire of circular cross section, a pair of recording structures, a magnetic circuit and a magnetizing winding for carrying magnetizing current individual to each of said pair of recording structures, said recording structures being oriented to produce magnetic fluxes in mutually perpendicular directions at the same location with respect to said wire, and means including network units connected to each of said windings for producing signals in each of said windings one of which is substantially in quadrature with respect to the other'over' a band of frequencies.

3. In a system. for recording sound, a. pair of magnetic circuits, means for generating two Signals from a source of signalling one of said sig-- nals being phase displaced with respect to the other, and means for energizing the first of saidmagnetic circuits with one of said generated signals and the second of said magnetic circuits with 5 the other of said generated signals.

nals and the second of said magnetic circuits with the other of said generated signals, and means for magnetizing a magnetic wire in accordance with said generated signals.

5. In a system for recording sound, a plurality of magnetic circuits, 2. source of signalling means comprising a plurality of phase shifting networks having phase shifting characteristics for generating a plurality of signals from said source of signalling one of said plurality of signals being substantially in quadrature with respect to another of said plurality of signals and means for energizing each of said magnetic units with one of said plurality of generated signals individual to each magnetic unit.

6. In a device for recording sound on magnetic wire, a wire of magnetizable material having a circular cross section, means for simultaneously magnetizing said wire in two mutually perpendicular transverse directions in accordance with two magnetizing signals derived from an input signal, one of said magnetizing signals difiering in phase from the other of said magnetizing sig- 7 nals by substantially 90 over a band of'frequencies.

7. In a system for recording sound on a magnetic wire of circular cross-section, a pair of re cording structures each comprising a magnetic circuit and a magnetizing winding for carrying magnetizing current, said recording structures being oriented to produce magnetic fluxes in mutually perpendicular directions at the same location, two phase-shifting networks each having input and output terminals, said input terminals being connected in parallel to form a common input connection, the output terminals of one of said phase shifting networks being connected to one of said magnetizing windings, the output terminals of the other of said phase shifting circuits being connected to the other of said magnetizing windings, and said phase shifting networks having phase shifts which differ by substantially 90 over a band of frequencies.

8. A magnetic wire record of circular cross section having signals of a series of frequencies received thereon in a series of helical paths around the wire, each of said recorded frequencies having a pitch individual thereto and being along the longitudinal axis.

. 9. The method of recording signals of a series of frequencies on a magnetic wire of circular cross-section which comprises causing the magnetization for each frequency to progress helically independently of all the other frequencies along the wire as the signal frequencies are impressed on the wire.

10. The method of recording signals on a magnetic wire of circular cross-section which comprises recording a signal of a plurality of frequencies in a helical path around the wire as the wire progresses longitudinally, the pitch of the helix along the wire being such that for each frequency recorded, the magnetization rotates completely around the wire in one period of that frequency.

11. A magnetic wire record of circular crosssection having signals of a plurality of frequencies recorded thereon on a corresponding plurality of helical paths, the pitch of each of the helices along the wire being such that in one period of any one of the frequency being recorded, the magnetization therefor has rotated once around the wire.

12. A magnetic wire record of circular crosssection having signals comprised of a plurality offrequeiicies recordedathe'rein, each frequency being recorded in a helical manner independently of the other frequencies, and for each frequency the pitch of the helix along the wire being such that in one, period of the frequency being recorded, the magnetization has rotated once around the wire.

13. The method of recording signals in a magnetic wire which comprises producing two independent signals from a single source at substantially phase displaced from each other and magnetizing a wire simultaneously by fluxes generated by said signals.

14. The method of recording signals in a magnetic wire of circular cross-section which comprises producing signals substantially 90 phase displaced from each other generating magnetic fluxes substantially 90 space displaced from each other and magnetizing said wire while said wire is moving longitudinally past said fluxes to produce a helical recording on said wire.

15. The method of recording signals in a magnetic wire of circular cross-section which comprises producing signals phase displaced from each other generating magnetic fluxes space displaced from each other by angles substantially equal to the phase displacement of the signals and magnetizing said wire while said wire is moving longitudinally past said fluxes to produce a helical recording on said wire.

HOWARD E. TOMPKINS. WILLIAM E. BRADLEY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS- Number Name Date 1,865,200 Mathias June 28, 1932 1,949,409 Cohen Mar. 6. 1934 2,245,286 Marzocchi June 16, 1941 2,251,300 Star Aug. 5, 1941 2,272,821 Roys Feb. 10, 1942 2,334,510 Roberts Nov. 16, 1943 2,425,213 Sunstein Aug. 7, 1947 2,458,315 Sunstein Jan. 4, 1949 FOREIGN PATENTS Number Country Date 651,990 France Mar. 1, 1929 594,991 Germany Mar. 24, 1934 

